A. R. Wilfley & Sons, Inc., the assignee of this invention, is noted for the innovative design and development of centrifugal pumps which are characterized by being of the fluid or hydraulic sealing type; i.e., do not require a packing gland or mechanical seal bearing directly against a rotating part, such as, the drive shaft, but are capable of effectively sealing against leakage when the pump is not in operation. For example, U.S. Pat. No. 1,976,532 and U.S. Pat. No. 2,660,487 to Wilfley are directed to frictionless pumps having no packing gland around the pump drive shaft but including a check valve assembly around the shaft which will open and close an annular gap between the shaft and pump housing in order to maintain the gap open while the pump is running and keep it closed when the pump is at rest. When the pump is running, one or more expellers draws fluid through the gap to generate counteracting hydraulic pressure or a seal to prevent leakage of the working liquid or slurry past the expeller and through the gap when the pump is in operation. The check valve assembly has a speed-responsive actuating mechanism that overcomes the normal urging of the valve into a sealed position to open the gap in response to a predetermined speed of rotation of the drive shaft by causing weighted levers to overcome the urging of the spring. Numerous improvements have been made by A. R. Wilfley & Sons, Inc. in this type of pump design and construction as exemplified by other U.S. Pat. Nos. 2,581,504; 3,137,237 to Zagar et al.; and U.S. Pat. No. 3,652,180 to Choquette et al. Among other problems associated with pump designs of the type described is that the weighted levers are normally exposed to the working fluid and any contaminants or foreign particles in the fluid. Moreover, liquid build-up in the pump casing behind the expeller region during intervals of starts and stops has necessitated leakage of that liquid away from the pump and is of particular concern when contaminants are present in the liquid.
It is therefore proposed in accordance with the present invention to overcome the problem of leakage by substantially reducing the volume of liquid retained in the reservoir region and to be able to store the liquid that does return to the reservoir or seal housing without leakage each time that the pump is started or stopped. When the pump is started, the valve assembly is actuated to open and an expeller ring will then discharge to the the extent of completely expelling the liquid stored in the reservoir. In accordance with conventional practice, another expeller member or members develops a hydraulic seal to prevent leakage back through the expeller region. Further, it is proposed to completely isolate the actuating mechanism of the valve assembly from the liquid in the reservoir but which mechanism will act in a positive manner in response to starting of the pump to overcome urging of a spring-loaded valve assembly to open and make possible the discharge of liquid by the expeller from the reservoir.